1. Field of the Invention
The present invention relates generally to thermal spraying and, more specifically, to thermally sprayed articles and a method of making thermally sprayed articles.
2. Description of the Related Art
It is known to thermally spray articles. In thermal spraying, a thermally sprayed article is produced using a wire-arc spraying. In wire-arc spraying, electric current is carried by two electrically conductive, consumable wires with an electric arc forming between wire tips of a wire arc gun. A high-velocity gas jet blowing from behind the consumable wires strips away the molten metal, which continuously forms as the wires are melted by the electric arc. The high-velocity gas jet breaks up or atomizes the molten metal into finer particles in order to create a fine distribution of molten metal droplets. The atomizing gas then accelerates the molten metal droplets away from the wire tips to the article where the molten metal droplets impact the article to incrementally form a deposit on the article.
Thermal spraying is typically used for tribological applications and for component manufacturing. Some of the current applications include engine block bore coatings, valve seat inserts, steering stop coatings, body joint fillers and tooling. The Achilles"" heel of thermally sprayed materials, particularly when considered for component manufacturing (such as in tooling and valve seat inserts for example) is their machineability. During the thermal spraying process, the molten metal droplets are formed and stacked on the article to be thermal sprayed. As a result, the machining of thermally sprayed articles generally involve a lot of interrupted bi-metallic and ceramic/metal cuts. This is detrimental to tool life and poses a problem of reproducibility of machined surfaces. Moreover, since most of the molten metal droplets generally have particle sizes ranging from 2 to 50 micrometers, the chips produced are of the same magnitude. As a result, expensive ultra-filtration operations are often required to capture the machined chips. Even then, machining-generated ultrafine particles (less than a few micrometers in size) generally remain in machining fluids and reduce the-life of coolant recirculation pumps.
Although the above process for thermally spraying articles has worked well, it is desirable to improve the machinability of thermally sprayed articles. It is also desirable to produce a thermally sprayed article that has larger chips when machined. It is further desirable to produce a thermally sprayed article that has reduced cost.
Accordingly, the present invention is a thermally sprayed article. The thermally sprayed article has an inner layer of a metal material with a first predetermined thickness. The thermally sprayed article also has an outer layer formed on the inner layer of a composite made of a polymer and the metal material with a second predetermined thickness.
Also, the present invention is a method of making a thermally sprayed article. The method includes the steps of providing an article to be thermally sprayed. The method also includes the steps of thermally spraying a metal material against the article to form an inner layer having a first predetermined thickness and co-depositing a polymer and the metal material against the inner layer to form an outer layer having a second predetermined thickness.
One advantage of the present invention is that a highly machinable thermally sprayed article and method of making the article is provided. Another advantage of the present invention is that the method improves the machinability of thermally sprayed articles by modifying the outer layer to be machined. Yet another advantage of the present invention is that the method decreases the hardness and increases the plasticity and lubricity of the outer layer while the hardness of the inner layer remains unchanged. Still another advantage of the present invention is that the method provides a way to connect splats and avoid interrupted cuts of the thermally sprayed article. A further advantage of the present invention is that the method produces thermally sprayed articles that, when machined, have long and curled machined chips that are easy to recover.
Other features and advantages of the present invention will be readily appreciated, as the same becomes better understood after reading the subsequent description taken in conjunction with the accompanying drawings.